Conformational studies and molecular characterization of the polysaccharide kefiran

Methods of study on conformation of polysaccharides from natural products: A review

Polysaccharides from natural products play multiple roles and have extensive bioactivities in life process. Bioactivities of polysaccharides (e.g., Lentinan, Schizophyllan, Scleroglucan, Curdlan, Cinerean) have a close relation to their chain conformation. Compared to other types of polysaccharides, the conformation of β-glucan has been studied more. The major research methods of conformation of polysaccharides from natural products (Congo red experiment, circular dichroism spectrum, viscosity method, light scattering method, size exclusion chromatography, atomic force microscope), corresponding experimental schemes, and the external factors affecting polysaccharide conformation were reviewed in this paper. These research methods of conformation have been widely used, among which Congo red experiment and viscosity method are the most convenient ones to study the morphological changes of polysaccharide chains.

Effect of subcritical water temperature on the structure, antioxidant activity and immune activity of polysaccharides from Glycyrrhiza inflata Batalin

In this study, the polysaccharide from Glycyrrhiza inflata Batalin extracted by hot water (HW-GP) was further physically modified with subcritical water to obtain novel polysaccharides (SW-GP). Comparative analysis was conducted to examine the disparities in conformation and bioactivity between HW-GP and SW-GP, aiming to precisely regulate the structure of the polysaccharides and enhance their bioactivity by controlling subcritical water temperature. The results showed that, compared with HW-GP, subcritical water modification (100-160 °C) not only significantly reduced the molecular weight of polysaccharides (from 5.586 × 105 g/mol to 1.484 × 105 g/mol), but also modulated the intermolecular interaction forces, which maintain the conformation of the polysaccharides, including electrostatic and hydrophobic interactions, thereby dynamically transforming the polysaccharide chain conformation from triple helix to random coil, and the strength of the chain conformation shifted from rigid to flexible. In addition, the modification of the SW-GP structure by subcritical water also enhanced its biological activity. SW-GP (140 °C) with low molecular weight and semi-rigid triple helix conformation showed the best scavenging effect on the DPPH, ABTS, and hydroxyl radicals, and exhibited excellent antioxidant activity. SW-GP (130 °C) with medium molecular weight and semi-rigid triple helix conformation significantly promoted the proliferation and phagocytosis of RAW264.7 cells, as well as increased the release levels of NO, TNF-α, IL-6, and IL-1β, and the immunomodulatory activity was much higher than that of other polysaccharides. These findings confirmed the feasibility of using subcritical water temperature as a regulatory feature for the structure and bioactivity of glycyrrhiza polysaccharides, which may have reference significance for the modification of polysaccharides with heightened bioactivity.

Physicochemical properties and solution conformation of polysaccharides from Toona sinensis (A. Juss) Roem leaves

In this study, two polysaccharide fractions (TSP-1 and TSP-2) were isolated from Toona sinensis leaves. The physicochemical properties and solution conformations of TSP-1 and TSP-2 were investigated. DSC and TG results showed that TSP-1 and TSP-2 had thermal stability. The intrinsic viscosities of TSP-1 and TSP-2 solutions were 11.42 and 6.13 mL/g, respectively. Rheological results showed that the viscosities of TSP-1 and TSP-2 solutions were affected by polysaccharide concentration, Ca2+ and extreme pH. Furthermore, TSP-1 exhibited a weak gel behavior at the concentrations of 0.5 %-2.0 %, while TSP-2 showed a weak gel behavior at the concentration of 2 %. HPSEC-MALLS analysis revealed that the Rg values of TSP-1 and TSP-2 were 96.8 nm and 56.2 nm, respectively. Conformation analysis indicated that TSP-1 behaved as a sphere, while TSP-2 behaved like a rigid rod. These results suggest that TSP-1 and TSP-2 can be used as additives in food, pharmaceutical and cosmetic industries.

Effect of caseinate salt addition on the structural characteristics of kefiran systems

Sodium caseinates-kefiran systems were studied to explore whether any potential interactions between them might exist. The study was performed using low-deformation rheological techniques, which were dynamic and creep tests. The systems were prepared under various experimental conditions such as heating and acidification. Besides, the structure development of the systems in relation to time was also monitored using oscillatory shear rheometry. The results indicated that the structural characteristics of the systems were mainly affected by the state of the caseinates such as the formation of aggregates and to a lesser degree by the interactions of kefiran molecules with the caseinates. Freeze-thaw treatment produced cryogels with good thermal stability and fairly satisfactory mechanical properties. The morphology of the caseinate-kefiran systems was also investigated by means of confocal laser scanning microscopy.

Fluorescence probe technique for determining the hydrophobic interactions and critical aggregation concentrations of Gleditsia microphylla gum, circular Gleditsia sinensis gum, and tara gum

Circular Gleditsia sinensis gum, Gleditsia microphylla gum, and tara gum are galactomannans (GMs) with similar mannose/galactose (M/G) molar ratios, which complicates the characterization of physicochemical properties using conventional methods. Herein, the hydrophobic interactions and critical aggregation concentrations (CACs) of the GMs were compared using a fluorescence probe technique, in which the I1/I3 ratio of pyrene indicated polarity changes. With increasing GM concentration, the I1/I3 ratio decreased slightly in dilute solutions below the CAC but decreased sharply in semidilute solutions above the CAC, indicating that the GMs formed hydrophobic domains. However, increases in temperature destroyed the hydrophobic microdomains and increased the CACs. Higher concentrations of salts (SO42-, Cl-, SCN-, and Al3+) promoted hydrophobic microdomain formation, and the CACs in Na2SO4 and NaSCN solutions were lower than those in pure water. Hydrophobic microdomain formation also occurred upon Cu2+ complexation. Although urea addition promoted hydrophobic microdomain formation in dilute solutions, the microdomains were destroyed in semidilute solutions and the CACs increased. The formation or destruction of hydrophobic microdomains depended on the molecular weight, M/G ratio and galactose distribution of GMs. Therefore, the fluorescent probe technique enables the characterization of hydrophobic interactions in GM solutions, which can provide valuable insight into molecular chain conformations.

Enhanced probiotic potential of Lactobacillus kefiranofaciens OSU-BDGOA1 through co-culture with Kluyveromyces marxianus bdgo-ym6

Introduction

Due to the increasing consumer demand for the development and improvement of functional foods containing probiotics, new probiotic candidates need to be explored as well as novel means to enhance their beneficial effects. Lactobacillus kefiranofaciens OSU-BDGOA1 is a strain isolated from kefir grains that has demonstrated probiotic traits. This species is the main inhabitant of kefir grains and is responsible for the production of an exopolysaccharide (EPS) whit vast technological applications and potential bioactivities. Research has shown that interkingdom interactions of yeast and lactic acid bacteria can enhance metabolic activities and promote resistance to environmental stressors.

Methods

Comparative genomic analyses were performed to distinguish OSU-BDGOA1 from other strains of the same species, and the genome was mined to provide molecular evidence for relevant probiotic properties. We further assessed the cumulative effect on the probiotic properties of OSU-BDGOA1 and Kluyveromyces marxianus bdgo-ym6 yeast co-culture compared to monocultures.

Results

Survival during simulated digestion assessed by the INFOGEST digestion model showed higher survival of OSU-BDGOA1 and bdgo-ym6 in co-culture. The adhesion to intestinal cells assessed with the Caco-2 intestinal cell model revealed enhanced adhesion of OSU-BDGOA1 in co-culture. The observed increase in survival during digestion could be associated with the increased production of EPS during the late exponential and early stationary phases of co-culture that, by enhancing co-aggregation between the yeast and the bacterium, protects the microorganisms from severe gastrointestinal conditions as observed by SEM images. Immune modulation and barrier function for recovery and prevention of flagellin-mediated inflammation by Salmonella Typhimurium heat-killed cells (HKSC) in Caco-2 cells were also measured. OSU-BDGOA1 in mono- and co-culture regulated inflammation through downregulation of pro-inflammatory cytokine expression and increased membrane barrier integrity assessed by TEER, FD4 permeability, and expression of tight junctions.

Discussion

The results of the study warrant further research into the application of co-cultures of yeast and LAB in functional probiotic products and the potential to increase EPS production by co-culture strategies.

Structural characterization of a homopolysaccharide produced by Weissella cibaria FMy 2-21-1 and its potential application as a green corrosion inhibiting film

Steel corrosion is a global issue that affects safety and the economy. Currently, the homopolysaccharide (HoPS) structure of a novel lactic acid bacterium (LAB) is under study, as well as its application as a green corrosion inhibitor. Weissella cibaria FMy 2-21-1 is a LAB strain capable of producing HoPS in sucrose enriched media. The isolated and purified HoPS was characterized by different spectroscopic analyses as a linear α-1,6 dextran adopting a random coil conformation, with high molecular weight and extended size in water. The polysaccharide showed a semi-crystalline organization, which is a requirement for film formation. Its biocoating showed a grainy network structure, with a slightly lesser hydrophobic role in the aqueous environment than in the ionic one. The electrochemical measurements of the steel-HoPS coating showed that the biopolymer layer acts as an anodic-type corrosion inhibitor, with high resistance to corrosion by water and with chloride ions which prevent pitting, a corrosion process typical of bare steel. Few reports have cited the application of LAB HoPS as corrosive coating inhibitors. This work is the first to explore the influence of a structurally characterized dextran from Weissella cibaria strain as a potential steel corrosion inhibitor in ionic environments.

Study of the effect of the addition of plasticizers on the physical properties of biodegradable films based on kefiran for potential application as food packaging

Spectroscopies analysis indicated that kefiran contains branched hexasaccharide repeating units. Neat kefiran films, 2 and 5% w/w of glycerol, d-glucitol, d-galactitol, d-mannitol, and d-limonene were incorporated as plasticizers. Neat and plasticized kefiran films were characterized by physical, thermal, mechanical, optical, and water solubilization properties. Neat kefiran had a glass transition temperature (T_g) of -20 ± 2 °C and, with the addition of plasticizers between -15 to -17 ± 2 °C. The values were close to the neat kefiran, and the results could be attributed to a lower amount of plasticizer used. The solubility of the glycerol plasticized films increases by 33% and decreased with the concentration of other plasticizers in comparison with the neat kefiran. d-glucitol and d-galactitol decreased the microhardness and Young's Modulus of films around 30% and 74% respectively, obtaining more flexible kefiran films. Kefiran based films could find applications as potential materials in the food-packaging industry.

An investigation of factors affecting the electrospinning of poly (vinyl alcohol)/kefiran composite nanofibers

This study aimed to investigate parameters affecting the electrospinning of poly (vinyl alcohol) (PVA)/kefiran composite nanofibers. Accordingly, PVA/kefiran composite nanofibers were produced using the electrospinning of PVA, kefiran blend solutions under various electrospinning parameters (such as applied voltage, nozzle-to-collector distance, and polymer injection rate), and solution parameters (such as the ratio of polymers). PVA and kefiran solutions were prepared in 8% and 6% w/w, respectively. Kefiran was blended with PVA solution in different proportions: 70:30, 60:40, 50:50, 40:60, and 30:70. According to the scanning electron microscope (SEM) images, kefiran mixed with PVA in 40:60 ratios produced the best result in nanofiber production. Then, device parameters such as voltage (12, 15, 18, and 20 kV), distance (120, 150, 170, and 200 mm), and polymer injection rates (1, 1.5, 2, and 2.5 mL/h) were changed. The investigation of SEM images showed that the optimal condition for the fabrication of nanofibers was 18 kV, 200 mm, and 1 mL/h. The nanofibers produced in the optimal condition were uniform without knots or adhesion in a small diameter. It was also found that concentration can be regarded as the most effective parameter affecting the diameter of nanofibers. Moreover, the transmission electron microscopy (TEM) image proved that phase separation did not occur between the two polymers.

GRAPHICAL ABSTRACT

Kefiran biopolymer extracted from fermented milk was used in fabrication of PVA/kefiran composite nanofibers using the electrospinning method.

Biomedical Applications of Bacterial Exopolysaccharides: A Review

Bacterial exopolysaccharides (EPSs) are an essential group of compounds secreted by bacteria. These versatile EPSs are utilized individually or in combination with different materials for a broad range of biomedical field functions. The various applications can be explained by the vast number of derivatives with useful properties that can be controlled. This review offers insight on the current research trend of nine commonly used EPSs, their biosynthesis pathways, their characteristics, and the biomedical applications of these relevant bioproducts.

Green synthesis of nano-Al2O3, recent functionalization, and fabrication of synthetic or natural polymer nanocomposites: various technological applications

Environmentally friendly fabrication of nano-Al₂O₃, recent functionalization, and preparation of polymer nanocomposites including natural and man-made polymers with various industrial applications are reviewed.

Octenyl succinylation of kefiran: Preparation, characterization and functional properties

In this study, kefiran was esterified with octenyl succinic anhydride (OSA). The esterification reaction variables including pH (8.5), kefiran concentration (5% (w/w)), OSA concentration (12% (w/w)), temperature (~38 °C) and reaction time (~80 min) were found as optimum points to achieve the maximum degree of substitution (DS) (0.041 ± 0.002). Kefiran-OSA samples with DS of 0.021 (FDA suggested DS) and 0.041 (maximum DS) were prepared and compared with unmodified kefiran in all experiments. FTIR and ¹H NMR spectroscopies proved the grafting of OSA on kefiran structure. XRD analysis revealed that with increase in DS, the physical state of kefiran to be more amorphous. In addition, the esterification modification led to a decrease in the degradation temperature and an increase in the apparent viscosity based on the obtained data from thermal analysis and viscosity measurement. The results of the foaming and emulsifying properties confirmed the improvement in surface properties of the modified kefiran. The frequency sweep test illustrated that with an increase in DS, the viscoelastic behavior of the kefiran cryogels to be more viscous. It can finally be stated that the modification with OSA was a high potential strategy to extend the industrial applications of the kefiran.

Prospect of Polysaccharide-Based Materials as Advanced Food Packaging

The use of polysaccharide-based materials presents an eco-friendly technological solution, by reducing dependence on fossil resources while reducing a product's carbon footprint, when compared to conventional plastic packaging materials. This review discusses the potential of polysaccharides as a raw material to produce multifunctional materials for food packaging applications. The covered areas include the recent innovations and properties of the polysaccharide-based materials. Emphasis is given to hemicelluloses, marine polysaccharides, and bacterial exopolysaccharides and their potential application in the latest trends of food packaging materials, including edible coatings, intelligent films, and thermo-insulated aerogel packaging.

Dynamic High-Pressure Microfluidization-Treated Pectin under Different Ethanol Concentrations

We previously reported that dynamic high-pressure microfluidization (DHPM) can degrade pectin in aqueous solution. In this study, we further investigated the effect of DHPM on pectin in water-ethanol systems. In the absence of DHPM treatment, it was found that pectin exhibited increased average particle size and unchanged average molecular weight, but a decline in reducing-sugar-ends content with the increase of ethanol concentrations (0⁻10% v/v). These results indicated that the addition of ethanol induced aggregation of pectin. During DHPM treatment, pectin underwent disaggregation and degradation under all measured ethanol concentrations. Disaggregation was enhanced but degradation was weakened with the increase of ethanol concentration. FT-IR and UV spectra indicated that demethylation but no β-elimination occurred in the water-ethanol system during DHPM. Finally, the mechanism of DHPM-induced disaggregation and degradation of pectin under a water-ethanol system was updated. This work may help us to find a suitable condition for reducing the degradation of pectin during the process of homogenization.

Polyguluronate sulfate (PGS) attenuates immunological liver injury in vitro and in vivo

Hepatocyte damage, especially immunological liver injury, is a key process in the pathogenesis of hepatitis virus-induced liver diseases. The aim of this study was to investigate the protective effects of polyguluronate sulfate (PGS) against immunological liver damage. The results showed that PGS significantly reduced the H₂O₂-induced oxidative stress and increased the cell viability in HepG2 hepatocytes. PGS also suppressed the production of malondialdehyde (MDA), lactate dehydrogenase (LDH), TNF-α, and IL-6, while up-regulating the activity of SOD in HepG2 cells. Further, PGS (150 and 300mg/kg/day) significantly attenuated the elevation of serum glutamate pyruvate transaminase (ALT), aspartate aminotransferase (AST), total bilirubin (TBiL), in addition to liver MDA and NO levels in Con A-induced immunological liver injury within mice (P<0.05). Significant improvements of organ indexes (liver, spleen, and thymus) were observed in PGS-treated mice. PGS also significantly reduced the disorganization of hepatocytes and decreased the inflammatory cell infiltration caused by Con A treatment, suggesting that PGS was able to attenuate Con A-induced liver injury. In conclusion, PGS possesses significant hepatoprotective effects on immunological liver injury in vitro and in vivo, and this may be related to its antioxidant activities.